AboutArrays.js

// require('jasmine.js');
describe('About Arrays', function () {
  // We shall contemplate truth by testing reality, via spec expectations.
  it('should create arrays', function () {
    const emptyArray = []
    // console.log('here in arrays');
    expect(typeof (emptyArray)).toBe('object') // A mistake? - http:javascript.crockford.com/remedial.html
    // console.log(emptyArray.length);
    expect(emptyArray.length).toBe(0)

    const multiTypeArray = [0, 1, 'two', function () { return 3 }, { value1: 4, value2: 5 }, [6, 7]]
    expect(multiTypeArray[0]).toBe(0)
    expect(multiTypeArray[2]).toBe('two')
    expect(multiTypeArray[3]()).toBe(3)
    expect(multiTypeArray[4].value1).toBe(4)
    expect(multiTypeArray[4].value2).toBe(5)
    expect(multiTypeArray[5][0]).toBe(6)
  })

  it('should understand array literals', function () {
    const array = []
    expect(array).toEqual([])

    array[0] = 1
    expect(array).toEqual([1])

    array[1] = 2
    expect(array).toEqual([1, 2])

    array.push(3)
    expect(array).toEqual([1, 2, 3])
  })

  it('should understand array length', function () {
    const fourNumberArray = [1, 2, 3, 4]

    expect(fourNumberArray.length).toBe(4)
    fourNumberArray.push(5, 6)
    expect(fourNumberArray.length).toBe(6)

    const tenEmptyElementArray = new Array(10)
    // console.log(tenEmptyElementArray.length);
    expect(tenEmptyElementArray.length).toBe(10)

    tenEmptyElementArray.length = 5
    console.log(tenEmptyElementArray.length)
    expect(tenEmptyElementArray.length).toBe(5)
  })

  it('should slice arrays', function () {
    const array = ['peanut', 'butter', 'and', 'jelly']

    expect(array.slice(0, 1)).toEqual(['peanut'])
    expect(array.slice(0, 2)).toEqual(['peanut', 'butter'])
    console.log(array.slice(3, 0))
    expect(array.slice(2, 2)).toEqual([])
    expect(array.slice(2, 20)).toEqual(['and', 'jelly'])
    expect(array.slice(3, 0)).toEqual([])
    expect(array.slice(3, 100)).toEqual(['jelly'])
    expect(array.slice(5, 1)).toEqual([])
  })

  it('should know array references', function () {
    const array = ['zero', 'one', 'two', 'three', 'four', 'five']

    function passedByReference (refArray) {
      refArray[1] = 'changed in function'
    }
    passedByReference(array)
    expect(array[1]).toBe('changed in function')

    const assignedArray = array
    assignedArray[5] = 'changed in assignedArray'
    expect(array[5]).toBe('changed in assignedArray')

    const copyOfArray = array.slice()
    copyOfArray[3] = 'changed in copyOfArray'
    expect(array[3]).toBe('three')
  })

  it('should push and pop', function () {
    const array = [1, 2]
    array.push(3)

    expect(array).toEqual([1, 2, 3])

    const poppedValue = array.pop()
    expect(poppedValue).toBe(3)
    expect(array).toEqual([1, 2])
  })

  it('should know about shifting arrays', function () {
    const array = [1, 2]

    array.unshift(3)
    expect(array).toEqual([3, 1, 2])

    const shiftedValue = array.shift()
    expect(shiftedValue).toEqual(3)
    expect(array).toEqual([1, 2])
  })
})